This invention relates to a mechanism for monitoring operating conditions of an internal combustion engine to produce a signal for controlling fuel injection system parameters. The mechanism senses the magnitude of combustion chamber peak pressure and the time occurrence of the peak pressure on a pressure-time curve. The mechanism also detects the rate of pressure rise curve during the compression/power stroke to permit adjustment of the fuel injection timing, ignition timing, and the fuel quantity required to bring the rate of combustion pressure rise and peak cylinder pressure within acceptable limits for the given power demand. Included in the mechanism is a microcomputer that contains a read-only memory containing optimum pressure-time curves for a range of engine loads and engine speeds. The predetermined stored curves are selectively compared with sensed values of engine load and speed to generate desired fuel injection parameter and ignition actuation/timing control signals. In some respects, the mechanism has functional similarities to mechanisms disclosed in U.S. Pat. No. 4,250,858 to Jeenicke et al., U.S. Pat. No. 4,257,377 to Kingugawa et al., and U.S. Pat. No. 4,309,971 to Chiesa et al. Those patents disclose microcomputers for at least partially controlling the combustion cycles of internal combustion engines.